Method and apparatus for calcining particulate mineral materials

ABSTRACT

A method and apparatus for the improved calcining of particulate mineral materials adapted particularly for the vibratory type kiln wherein a bed of particulate material is intermittently vibrated or reciprocated during the burning of a gaseous fuel therein. In the present invention, gaseous fuel and preheated air are separately introduced into the particulate material bed at a plurality of regularly spaced locations. This permits a uniform penetration of the air and fuel into the interstices of the particulate material and a consequent uniform burning of the fuel throughout the material bed. As a result, a deeper bed may be maintained, and a more uniform product is obtained at a faster rate and with lower fuel consumption.

[ 51 Feb. 22, 1972 United States Patent Corson et al.

[54] METHOD AND APPARATUS FOR Primary Examiner-John J. Camby CALCININGPARTICULATE MINERAL Attorn y-Rowen and Howson MATERIALS Bolton L.Corson, Philadelphia; Budd R. Royer, Lansdale, both of Pa.

[57] ABSTRACT A method and apparatus for the improved calcining of par-[72] inventors:

[73] Assignee: Comm Plymouth Meet ticulate mineral materials adaptedparticularly for the vibratory type kiln wherein a bed of particulatematerial is intermittently vibrated or reciprocated during the burningof a gaseous Apr. 3, 1970 [21] Appl.No.: 25,392

[22]. Filed:

' fuel therein. In the present invention, gaseous fuel and preheated airare separately introduced into the particulate material bed at aplurality of regularly spaced locations. This permits a uniformpenetration of the air and fuel into the interstices of the particulatematerial and a consequent uniform burning of the fuel throughout thematerial bed. As a result, a deeper bed may be maintained, and a moreuniform product is obtained at a faster rate and with lower fuelconsumption.

[56] References Cited UNITED STATES PATENTS 11 Claims, 8 Drawing Figures3,417,978 12/1968 Suzukawa et al. ...........23/21 A a e [a 0 O O O O OO O O O O PATENTEDFEB 22 I972 SHEET 1 OF 2 INVENTORSI BOLTON L.CORSONBUDD R. ROYER BY WW '4 FIGS.

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METHOD AND APPARATUS FOR CALCINING PARTICULATE MINERAL MATERIALS Thepresent invention relates generally to the calcining of particulatemineral material and relates more particularly to a method and apparatusfor improving the calcining of intermittently agitated beds ofparticulate material by providing a more uniform burning of a gaseousfuel within the material bed.

Although the present invention is broadly applicable to the calcining ofmineral materials, it is anticipated that its primary application willbe in the calcining of limestone, a necessary operation in theproduction of quicklime. In the present application, the invention willaccordingly be presented in the environment of limestone calciningoperations although it will be apparent that the method and apparatusemployed can equally well be applied to the treatment of othermaterials.

In the calcining of high-calcium limestone, which is essentially calciumcarbonate, the stone is heated to the temperature of disassociation ofthe carbonate whereupon it is broken down into quicklime and carbondioxide. The stone particles must be maintained at the calciningtemperature above approximately l,700 F. for a sufficient time to permitthe disassociation process to penetrate to the interior of theparticles.

The calcining operation is extremely critical since if the calciningtemperature or retention time in the kiln is insufficient, the stoneparticles will retain a center core of uncalcined carbonate stone, anundesirable product which is known as underburned lime. If the calciningtemperature is too high or the retention time too long, the stone tendsto shrink and densify, decreasing the reactivity of the lime. Thisundesirable product is known as hard-burned lime. The production of athoroughly calcined soft-burned lime can only be obtained by a carefulcontrol of the calcining operations including the stone temperature,retention time in the kiln, manner in which the particles move throughthe kiln, uniformity of particle size, etc.

The kilns presently in commercial use for calcining lime are of severaltypes. Principally, these include rotary kilns, wherein the material iscontinuously tumbled as it passes down an inclined rotating cylinder,and vertical or shaft kilns wherein the material drops verticallythrough a kiln shaft through various treating zones. The characteristicadvantages and disadvantages of the several types of limestone kilns arewell known. In a rotary kiln, the gaseous fuel is not burned within thematerial bed but is burned in the cylindrical furnace over the bed, andthe heating effect obtained is primarily by radiation as the limestoneparticles are tumbled. In the vertical kiln, the fuel burning may takeplace within the bed of material but tends to stratify with a resultantuneven calcining of the stone.

The present invention pertains to a more recent type of kiln known as avibratory kiln wherein a gaseous fuel is burned within a bed of materialwhich is intermittently agitated to insure a relatively uniform burningof the stone and to move the stone through the calcining region. A'preferred type of kiln for practicing the invention is disclosed in U.S.Pat. No. 3,250,520, issued on May 10, I966. The invention may also beapplied to a kiln of the type shown in U.S. Pat. No. 3,022,988, issuedon Feb. 27, 1962. Each of these patents is assigned along with thepresent application to a common assignee. In this type of kiln, theparticulate material passes in a bed of substantial depth through acalcining zone wherein the material is intermittently agitated orvibrated to provide by reason of the shape and inclination of the bedsupport a movement of the material through the calcining zone as well asan intermixing of the material particles. A gaseous fuel is introducedupwardly through the material bed supporting surface and is burnedwithin the bed to calcine the particles. In a typical example ofoperation of this type of kiln, the material is subjected to periods ofvibration or agitation followed by periods of rest. The length of theseperiods depends on the size and character of the stone as well as thedegree of temperature of the combustion air, length of the kiln, etc.However, in a typical design the rest period is usually about one minuteand the agitation period seconds.

Although vibratory kilns have been successfully operated on a commercialscale for a number of years, it has now been found that the quality ofthe product, the volume output, and the thermal efficiency of the kilncan be markedly improved by the relatively simple method and apparatusof the present invention. As indicated above, the present improvementrelates to the burning of the gaseous fuel in the material bed. In theprior vibratory kilns, the gaseous fuel and the combustion supportingair were introduced to the bed of particulate material throughconcentric inlet ports in the material support surface. An arrangementof this type is shown in detail in U.S. Pat. No. 3,250,520 in FIG. 13.With the fuel and air introduced at the same points, a very hottorchlike flame resulted at each combined air and fuel inlet, whichflame tended to drive in a torchlike manner up through the bed ofmaterial, sometimes emerging above the bed with a consequent loss ofheat to the stack. The stone particles in the path of and adjacent tothe flame would receive considerably more heat than particles moreremote therefrom, and an uneven calcining of the stone resulted.

Furthermore, with the prior structures, the stone particles wouldfrequently lodge directly above the fuel and air inlet ports whichprevented the fuel and air from passing up into the material bed. Attimes, the fuel turned downwardly and heated the hollow burner plates,such as shown in U.S. Pat. No. 3,250,520 to such a degree that the gascracked and formed carbon which blocked the gas outlet ports. Thisphenomenon can occur at approximately l,l00-l,300 F. with most naturalgases. The tendency for port blockage to occur increased with theincrease in the depth of the material bed and, therefore, it wasmandatory that the limestone bed be maintained at a comparativelyshallow depth in the calciner. A shallow material bed, however,increased the tendency for the gases to pass through the bed and exit athigh temperatures to the preheater which in turn increased thedifficulties of maintaining the tables, hoods, and feeding mechanisms inthe preheater. The penetration of the gas through the bed is readilyunderstood in view of the fact that the gas is introduced at pressuresas high as 20 pounds while the air is seldom supplied at over 1 pound.

In the present invention, the gas inlet ports in the bedplatessupporting the material are spaced from the air inlet ports therebyindependently introducing gaseous fuel and preheated combustionsupporting air into the material bed. With this arrangement, the fueland air penetrate the interstices of the entire particulate bed and burnin a uniform manner throughout the bed. There are no hot spots directlyabove thefuel inlets since these regions are the farthest spaced fromthe air inlets and burn with a rich controlled flame. There is nopossibility of the gas burning within the air inlet region shouldmaterial particles become lodged directly over the gas inlet ports. If apiece of material blocks a gas or air port, the flow of gas or airthrough that port is simply stopped until the port is cleared during thenext shaking operation.

It has been found that by using the present separated gas and air inletarrangement, a substantially deeper bed of material may be maintained inthe kiln and this increase in depth permits an increase in the volumeand pressure of the gas supplied to the bed. A much more uniformtemperature condition is produced throughout the bed, and the depth ofthe bed eliminates the tendency for the gases to pass through and burnabove the bed. As a result of the permissible increase in bed depth, theoutput of the kilns has in all cases been greatly increased and in somecases by as much as 50 percent. At the same time, the fuel consumptionper ton is substantially lower since the burning of the fuel above thebed is minimized. In a typical installation, the fuel consumption perton was lowered by the present invention from 6.5 to 5.5 million BTUsper ton. The more uniform burning of the fuel with the present inventionnaturally produces a more uniform calcining of the stone particles. Theoccurrence of underburned or hardburned particles is substantiallyeliminated and production consequently increased.

It is accordingly a first object of the present invention to provide animproved method and apparatus for the calcining of particulate mineralmaterials characterized by the burning of a gaseous fuel within avibrated material bed.

A further object of the invention is to provide a method and apparatusas described which permits the calcining of a relatively deep bed ofmaterial thus increasing the output of a conventional vibratory kiln byas much as 50 percent.

Another object of the invention is to provide a method and apparatus asdescribed which by providing a more uniform burning of the materialsubstantially eliminates the occurrence of underburned or hard-burnedparticles.

A still further object of the invention is to provide a method andapparatus as described which substantially reduces the fuel consumed perton of material processed.

A still further object of the invention is to provide a method andapparatus as described which provides a more controlled calciningoperation and hence an improved quality product.

Another object of the invention is to provide a method and apparatus asdescribed which may be readily applied to existing vibratory kilns.

Additional objects and advantages of the invention will be more readilyapparent from the following detailed description of embodiments thereofwhen taken together with the accompanying drawings in which:

FIG. 1 is a front elevational view of a conventional vibratory kilnwhich has been modified to incorporate the improvement of the presentinvention;

FIG. 2 is an enlarged end elevational view of the kiln taken along line2-2 of FIG. 1;

FIG. 3 is an enlarged view partly in section taken along line 3-3 ofFIG. 2 and showing the bed of particulate material as it moves throughthe calcining zone during vibration of the kiln;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3 showing a planlayout of the present burner pad assemblies and the fuel manifoldconnections;

FIG. 5 is an enlarged plan view of one of the burner pad assemblies ofthe kiln of FIGS. 1-4;

' FIG. 6 is a side elevational view of the burner pad assembly of FIG.5;

FIG. 7 is an enlarged partial sectional view taken along line 77 of FIG.5 showing details of the air and gas inlet ports; and

FIG. 8 is a partial plan view of a modified form of burner pad assembly.

Referring to the drawings and particularly to FIGS. 1 and 2 thereof, avibratory kiln is illustrated which is of the identical type shown anddescribed in the above-mentioned U.S. Pat. No. 3,250,520, issued May 10,1966, the disclosure of which is hereby incorporated by reference. Sincethe structure and operation of this kiln are completely described inthat patent, only a summary is presented herebelow. The identifyingnumerals and indicia utilized in the patent will for convenience besimilarly applied in the present case.

The vibratory kiln includes a calcining section A and a preheatingsection B, the generally cylindrical calcining section being suitablymounted on supporting frames 140 for vibratory or reciprocatory motionin an inclined plane as intermittently provided by motor 186 driving theeccentric drive unit 194. The flexible connector 114 between thecalcining section A and preheating section B maintains a sealed paththrough which the material to be calcined may drop under gravity forceinto the calcining section. A continuous conveyor apparatus 34 carriesthe particulate material, for example limestone, into the sizer 40 whichseparates the fines and discharges the material of a given predeterminedminimum size into hopper 46 and thence the preheater B.

In kiln operation, the material passing from the preheater drops intoone end of the calcining section and forms a bed of material into whicha gaseous fuel and air are introduced from below. The continuingintroduction of material and the intermittent vibrating or shaking ofthe calcining section cause the material to gradually move toward theopposite end of the calcining section where it passes through adischarge opening 274. The depth of the bed, temperature of thecalcining section, the rate of introduction of the material, andfrequency and duration of the periods of vibration are carefullycontrolled to provide the optimum calcining temperature conditions andretention time for the particular material processed.

The improvement of the present invention involves the method andapparatus for introducing the gaseous fuel and preheated air into thematerial bed. As mentioned above, the bedplates 232 of the kiln of U.S.Pat. No. 3,250,520 are characterized by a plurality of concentric gasand air inlets as seen most readily in FIG. 13 of that patent. In thepresent invention, the plates 232 and associated burner plates 242 arereplaced by the burner pad assemblies 300 which extend in parallelrelation transversely across the calcining section to support thematerial bed. Each burner pad assembly 300 as shown in FIGS. 5-7comprises a rectangularly shaped bedplate 302 having a plurality of gasinlet ports 304 therein. A gaseous fuel is delivered into the inletports 304 through vertical gas tubes 306 connected with the horizontalpipes 308 which in turn lead into the header 310 beneath one end of theplate. As shown in FIG. 4, the burner pads are supplied with a gaseousfuel under pressure by the connection of pipes 312 leading into theheaders 310 with a main fuel manifold 314 by means of couplings 316. Themanifold 314 is connected to fuel conduit 262 which leads to a suitablefuel source.

Spaced geometrically around the gas inlet ports 303 are air inlet ports318 which comprise holes in the plate 302 of substantially largerdiameter than the gas inlet ports and which communicate with the airchambers 254 therebeneath which are supplied with preheated combustionsupporting air by the air conduits 258 as shown in FIG. 3.

For operation of the kiln with the described burner pad assemblies 300,a gaseous fuel is introduced into the material bed at a pressuredependent upon the depth of the bed but which might typically rangebetween 5 and 20 p.s.i. The preheated (400-600 F.) air is delivered totheair chambers 254 at a relatively low pressure, for example 30 inchesof water. The introduction of the gaseous fuel and preheated air throughthe separate spaced ports in the bedplate permits a penetration of theinterstices between the material particles by both the gas and air and aresultant uniform burning of the fuel-air mixture throughout thematerial. There are no hot spots above the fuel inlet ports which mighttend to hard-burn the stone, and the separate points of introduction offuel and air further minimize the possibility of the combustion takingplace above the material bed as is likely to happen with the old typeconcentric gas and air ports. As a result, the heat loss to the stackand the depreciation of the kiln and stack lining are substantiallyreduced thus decreasing maintenance costs and increasing the length oftime the kiln can be run between shutdowns for relining.

The preheating of the combustion air has been found to be necessary toproduce the desired uniform calcining action. The preferred temperaturerange of the preheated air is between 400-600 F. although it is expectedthat acceptable results could be obtained with somewhat higher or lowertemperatures.

The increased production obtainable from a kiln by using the presentinvention is realized primarily due to the permissible increase in thedepth of the bed of particulate material passing through the calciningsection. Bed depth in the range of 18-20 inches can be maintained usingthe present method and apparatus without prejudicing the uniformity ofthe calcining treatment. As a result, the tonnage output of a kiln canbe increased from 30 to 50 percent, and even higher production increaseshave been noted at some installations.

From an economic standpoint, the invention despite its apparentsimplicity thus provides rather striking improvements both in the outputcapabilities of a particular kiln as well as the cost per ton ofcalcining the material. As a further and equally important benefit, theproduct produced by the present method and apparatus is superior inuniformity to that produced by the kiln without the present improvement.The improved ability to control the calcining conditions andspecifically the minimizing of hard-burned lime is an importantadvantage of the invention.

In FIG. 8, a modified form of burner pad 300 is illustrated whichdiffers from the preferred pad 300 primarily in the arrangement of thefuel and air inlet ports. In the pad 300, the bedplate 302 is providedwith spaced rows of fuel inlet ports 304' which are connected with theunderlying pipes 308 as in the preferred embodiment. The fuel ports 304'are, however, somewhat more closely spaced, and tee air inlet ports 318are arranged in spaced rows on each side of each row of fuel ports.Accordingly, in the modified embodiment there is a pair of air inletports for each fuel inlet port, the fuel inlet port being disposedbetween and equidistant from each adjacent air inlet port.

In the preferred embodiment, each fuel inlet port is also spacedequidistant from a plurality of air inlet ports although the number andarrangements of the ports is different. A variety of arrangements of thefuel and air inlet ports is accordingly possible to permit the separateintroduction of fuel and air into the bed of material as describedabove. Ac' cordingly, the number of the fuel and air inlet ports, andthe shape and size of the ports may be varied within the concept of theinvention.

The term particulate material for purposes of the present inventiondenotes discrete pieces of solid mineral material which are notfluidized by the introduction or combustion of the air and fuel withinthe material bed, or by the agitation or vibration of the bed. If theparticle size were so small as to fluidize under the influence of thegas and air introduction or combustion, the efficiency of the presentmethod would be adversely affected since the material would be difficultto control and the dust which would develop especially during theperiods of vibration would result in serious heat and material losses.Some dust is inevitably formed during the calcining of the discreteparticles although it does not seriously affect the efficiency of theprocess. The size of the discrete pieces of material should be chosenaccordingly, and for the calcining of limestone a preferred size of theparticles is from to 1% inches screen size.

While the illustrated method and apparatus have shown a kiln wherein thematerial is advanced through a calcining zone by vibration perpendicularto the path of movement of the material, it will be obvious that thedirection of vibration is not important to the invention and that thevibration or agitation may effectively be applied in any direction suchas in the path of material movement. Alternately, an oscillatorymovement of the bed could be employed.

Although in the calcining of limestone the preferred gaseous fuel isnatural gas, other gaseous fuels could be satisfactorily employed andother fuels such as oil which would convert into the gaseous form uponentry into the material bed would also be suitable.

As evidenced by the differences between the calcining zones of theabove-referenced U.S. Pat. Nos. 3,250,520 and 3,022,988, the shape andarrangement of the calcining zone is not critical to the inventionprovided that support means is included for the support of a materialbed of substantial depth into which the gaseous fuel and preheated airmay be separately introduced at separate spaced locations.

We claim:

1. The method of calcining particulate mineral material comprising thesteps of disposing the material on support means in a calcining zone toform a nonfluidized bed of substantial depth, introducing a fluid fuelinto said bed of material through said support means at a plurality ofspaced locations, introducing preheated air into said bed of materialsthrough said support means at a plurality of spaced locations separatefrom and spaced from said fuel introduction locations, and vibratingsaid material support means to advance the material along apredetermined path through said calcining zone, said preheated air andfluid fuel penetrating and uniformly burning throughout the particulatematerial bed to provide a uniform controlled calcining of the material.

2. The method as claimed in claim 1 including the step of preheating theparticulate material prior to introduction of the material into saidcalcining zone.

3. The method as claimed in claim 1 wherein said material support meansis intermittently vibrated to advance the material through saidcalcining zone.

4. The method as claimed in claim 1 wherein said fuel is introduced intosaid material bed at locations spaced equidistant a plurality of airintroduction locations.

5. The method as claimed in claim 1 wherein said fuel comprises agaseous fuel.

6. A calcining kiln comprising a calcining zone, means including atleast one burner pad assembly adapted to support a nonfluidized bed ofparticulate material within said calcining zone, means for vibratingsaid material bed support means to advance said material along asubstantially predetermined path through said calcining zone, means forintroducing a fluid fuel and preheated air into the nonfluidized bed ofmaterial for combustion therewith, said latter means comprising aplurality of fuel inlet ports in said burner pad assembly connected witha source of fuel under pressure, and a plurality of air inlet ports insaid burner pad assembly separate and spaced from said fuel inlet portsand connected with a source of preheated air under pressure.

7. the invention as claimed in claim 6 wherein each said fuel inlet portis spaced equidistant a plurality of said air inlet ports.

8. In a calcining kiln having a calcining zone including means adaptedto support a nonfluidized bed of particulate material, means forvibrating the bed support means to advance the material along asubstantially predetermined path through said calcining zone, and meansfor introducing a fluid fuel and preheated air into the bed forcombustion therewithin, the improvement comprising means for introducingthe fluid fuel and preheated air into said material bed at a pluralityof separate spaced locations whereby the air and fuel penetrate anduniformly burn throughout the particulate material bed to provide auniform controlled calcining of the material, said means for introducingthe fuel and air into said material bed comprising at least one burnerpad assembly on which said bed of particulate material is supported,said burner pad assembly comprising a flat bedplate, a plurality ofspaced fuel inlet ports in said bedplate, means connecting said fuelinlet ports with a source of fluid fuel under pressure, a plurality ofair inlet ports in said bedplate, said air inlet ports being separateand spaced from said fuel inlet ports, and means connecting said airinlet ports with a source of preheated air under pressure.

9. The invention as claimed in claim 8 wherein each said fuel inlet portis spaced equidistant a plurality of said air inlet ports.

10. A calcining kiln comprising a calcining zone, means adapted tosupport a nonfluidized bed of particulate material within said calciningzone, means for preheating the particulate material prior to theintroduction of the material into said calcining zone, means forintermittently vibrating said material bed support means to advance saidmaterial along a predetermined path through said calcining zone, saidmaterial bed support means comprising a plurality of burner padassemblies, each said burner pad assembly comprising a flat bedplate,and means for introducing a gaseous fuel and preheated air into thenonfluidized bed of material for combustion therewithin, said lattermeans comprising a plurality of spaced fuel inlet ports in each saidburner pad bedplate, means connecting said fuel inlet ports with asource of gaseous fuel under pressure, a plurality of air inlet ports ineach said burner pad bedplate, said air inlet ports being separate andspaced from said fuel inlet ports, and means connecting said air inletports with a source of preheated air under pressure.

11. The invention as claimed in claim 10 wherein each said fuel inletport is spaced equidistant a plurality of said air inlet ports.

Patent No.

Column 2, line 10,

Column 5, line 12,

Column 6, line 22,.

Signed and sealed this (SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Dated Februarv 2 2 1972 Inv nt fl Bolton L.Coreon and Budd R. Rover It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

after "material" (second occurrence) insert --bed-.

change "tee" to --the-.

change "therewith" to -therewithin 11 th day I of July 1972. Q

ROBERT GOT'ISCHALK Commissioner of Patents FORM PO-105O (10-69)USCOMM-DC 60376-P69 :8 us. GOVERNMENT PRINTING OFFICE: I969 0366-33A

2. The method as claimed in claim 1 including the step of preheating theparticulate material prior to introduction of the material into saidcalcining zone.
 3. The method as claimed in claim 1 wherein saidmaterial support means is intermittently vibrated to advance thematerial through said calcining zone.
 4. The method as claimed in claim1 wherein said fuel is introduced into said material bed at locationsspaced equidistant a plurality of air introduction locations.
 5. Themethod as claimed in claim 1 wherein said fuel comprises a gaseous fuel.6. A calcining kiln comprising a calcining zone, means including atleast one burner pad assembly adapted to support a nonfluidized bed ofparticulate material within said calcining zone, means for vibratingsaid material bed support means to advance said material along asubstantially predetermined path through said calcining zone, means forintroducing a fluid fuel and preheated air into the nonfluidized bed ofmaterial for combustion therewith, said latter means comprising aplurality of fuel inlet ports in said burner pad assembly connected witha source of fuel under pressure, aNd a plurality of air inlet ports insaid burner pad assembly separate and spaced from said fuel inlet portsand connected with a source of preheated air under pressure.
 7. theinvention as claimed in claim 6 wherein each said fuel inlet port isspaced equidistant a plurality of said air inlet ports.
 8. In acalcining kiln having a calcining zone including means adapted tosupport a nonfluidized bed of particulate material, means for vibratingthe bed support means to advance the material along a substantiallypredetermined path through said calcining zone, and means forintroducing a fluid fuel and preheated air into the bed for combustiontherewithin, the improvement comprising means for introducing the fluidfuel and preheated air into said material bed at a plurality of separatespaced locations whereby the air and fuel penetrate and uniformly burnthroughout the particulate material bed to provide a uniform controlledcalcining of the material, said means for introducing the fuel and airinto said material bed comprising at least one burner pad assembly onwhich said bed of particulate material is supported, said burner padassembly comprising a flat bedplate, a plurality of spaced fuel inletports in said bedplate, means connecting said fuel inlet ports with asource of fluid fuel under pressure, a plurality of air inlet ports insaid bedplate, said air inlet ports being separate and spaced from saidfuel inlet ports, and means connecting said air inlet ports with asource of preheated air under pressure.
 9. The invention as claimed inclaim 8 wherein each said fuel inlet port is spaced equidistant aplurality of said air inlet ports.
 10. A calcining kiln comprising acalcining zone, means adapted to support a nonfluidized bed ofparticulate material within said calcining zone, means for preheatingthe particulate material prior to the introduction of the material intosaid calcining zone, means for intermittently vibrating said materialbed support means to advance said material along a predetermined paththrough said calcining zone, said material bed support means comprisinga plurality of burner pad assemblies, each said burner pad assemblycomprising a flat bedplate, and means for introducing a gaseous fuel andpreheated air into the nonfluidized bed of material for combustiontherewithin, said latter means comprising a plurality of spaced fuelinlet ports in each said burner pad bedplate, means connecting said fuelinlet ports with a source of gaseous fuel under pressure, a plurality ofair inlet ports in each said burner pad bedplate, said air inlet portsbeing separate and spaced from said fuel inlet ports, and meansconnecting said air inlet ports with a source of preheated air underpressure.
 11. The invention as claimed in claim 10 wherein each saidfuel inlet port is spaced equidistant a plurality of said air inletports.